1. Field of the Invention
The present invention relates to a deflection coil mounted on a deflection yoke for regulating the progressive direction of electric beams emitted from an electron gun for use in television receivers, display units or the like, and a fabrication method thereof.
2. Description of the Prior Art
In recent years, development of high resolution television receivers increasingly tends to require strict specifications relating to color mismatching, i.e., convergence of the cathode-ray tube screen. Under such tendency, it is earnestly desired that a deflection magnetic field be controlled more precisely. FIG. 1 shows an example of a bobbin for a saddle type deflection coil for use in a typical deflection yoke. The bobbin 2 is provided with a plurality of coil-winding grooves 5, on which, for example, a coil of wire 11 is wound in layers as shown in FIG. 2, to thereby form a deflection coil. The coil of wire 11 is formed from conductive wires (including litz wires) with an insulating layer 4 provided thereon which is coated with an adhesive about its periphery.
FIG. 2 is an enlarged view of one of the coil-winding grooves 5 shown in FIG. 1. In winding the coiling wire 11 on coil-winding grooves 5, the wire 11 is wound in layers by an automatic winding machine, one turn at a time, or several turns with the wires being unbundled or separated into single wires, whereby a deflection coil will be produced. Subsequently, the thus wound layered coil is energized with electricity, to heat and melt the adhesive applied about the insulating layer 4, so that the coil wires adhere to each other to form a deflection coil.
Such prior art deflection coil, however, suffers from difficulties: owing to variations in the stretching force acting on wire 11 as it is wound, and other reasons, the wire 11 is unequally displaced and biased as shown in FIG. 2. In other cases, the order of winding of wire 11 is altered and hence the desired winding pattern cannot be reliably achieved. Further, the bias of wire 11 forming the deflection coil differs from one coil to the next in mass production. Therefore, it would be impossible to regulate a deflection field with high precision with mass-produced coils. Additionally, mass-production makes the variation between coils larger, resulting in lowering of the yield, and hence the prior art winding method is disadvantageous in view of the cost. Even in the just-mentioned prior art method, the variations in the displacement and bias of wire 11 is reduced as the width of the coil-winding groove is narrowed to satisfy an original design, but this creates another problem of coil performance being deteriorated because of a reduced L/R ratio.
In order to eliminate such problems, the present applicant has previously proposed a deflection coil which is composed by forming a layer in which a plurality of adjoining conductive wires are arranged parallel in a row, and winding this layer in place of winding a single wire, turn by turn, as used to be practiced in the prior art.
Examples of layers (hereinafter called "wire ribbon") 15 include one that is composed as shown in FIG. 3A by arranging in parallel a plurality of conductive wires 8 of copper, aluminum or the like with an insulating layer 4 coated thereon, and adhering them using an adhesive 6; one that is composed as shown in FIG. 3B by arranging in parallel a plurality of conductive wires 8 with an insulating layer 4 coated thereon, and adhering together the wires on one side of an insulator sheet 7 of resin, etc., with an adhesive 6; one that is composed as shown in FIG. 3C by arranging and adhering together in parallel a plurality of conductive wires 8 formed with an insulating layer 4 and an adhesive layer 9; and one that is composed as shown in FIG. 3D by arranging a plurality of conductive wires in a contacting manner in a row, each wire being with an insulating layer 4 covered by a thermoplastic adhesive layer 20.
The conductive wires 8 forming the aforementioned wire ribbon 15 are arranged in parallel with one another in an orderly manner in a row, and therefore, each conductive wire 8 will not be displaced in wire ribbon 15, nor will the order of the wires be altered. As a result, by developing a deflection coil having a structure pertinent to using the thus constructed wire ribbon 15, it can be expected to produce a deflection coil free from the problems such as significant displacement of the conductive wires, and the like.
The present applicant herein has previously proposed a deflection coil in which wire ribbon 15 is wound in layers such that the cross-section of the layers forms a rectangular shape. The rectangular shape of the cross-section of wire ribbon 15 can be achieved as shown in FIG. 4 by forming bottom faces 10 of coil-winding grooves 5 having flanges 3 to make right angles with corresponding flange faces 13, and winding wire ribbon 15 in layers in parallel with the bottom face 10. The deflection coil formed with the wire ribbon 15 can be remarkably improved in its characteristics as compared with those in the prior art.
Meanwhile, when wire ribbon 15 is inserted into coil-winding groove 5, the width of wire ribbon 15 would ideally be the same with that of coil-winding groove 5, but in practice of insertion, the width of wire ribbon 15 exhibits dispersion, so that wire ribbon 15 may possibly be wider than the groove. In such a case, the wire ribbon 15 would be deformed to be inserted into coil-winding groove 5. Accordingly, a margin or clearance would be provided between wire ribbon 15 and each side wall face of groove 5.
Nevertheless, if there exists such a clearance as mentioned above when wire ribbon 15 is inserted in coil-winding groove 5, there is a concern that side ends of layered wire ribbons 15 would not be flush to one another, as shown in FIG. 5, because of being wound in a nesting manner when wire ribbon 15 is wound in layers. Such nesting layers of wire ribbon 15 might make it difficult to realize precise control of a deflection magnetic field formed by the deflection coil.
Further, as shown in FIG. 4, when the aforementioned wire ribbon 15 is wound in this manner in layers on each of coil-winding grooves 5 formed on bobbin 2, all the cross-sections of layered coils of wire ribbon 15 become rectangular. Accordingly, neighboring coil-winding grooves 5 create on their sides of bottom faces 10 useless step portions 14 that would have no wound coil, and wire ribbon 15 forms spaces 12 inside coil-winding groove 5 as shown in FIG. 5. In addition, there occurs a concern that the grooves to be formed on the bobbin becomes less in number since the grooves require large groove widths. These problems lower the space factor of wires for the deflection coil, and the presence of the step portions would make assembly more difficult when the coil is fabricated into a deflection yoke.
If the width of coil-winding grooves 5 and the width of wire ribbon 15 are made smaller in order to reduce irregularity or nesting of layers of wire ribbon 15 as much as possible, the precision of a winding machine for winding wire ribbon 15 into coil-winding groove 5 must be greater, and this requires that the input data for the winding machine should additionally include, for example, the sequence of identifying positions in which wire ribbon 15 is wound and other factors, thus expanding the input data to become more complicated. This method also presents difficulty in preparing forming dies for bobbins and metal dies for sizes of coil wires.